The present invention builds on a method for the production of a or disk-shaped workpiece based on a dielectric substrate, which production method comprises the treatment in a plasma process volume, formed between two opposing electrode faces in a vacuum receptacle.
The present invention builds on a method for the production of a disk-form workpiece based on a dielectric substrate, which production method comprises the treatment in a plasma process volume, formed between two opposing electrode faces in a vacuum receptacle.
Definition
We are defining “electrode face” as a surface freely exposed to the plasma process volume.
In said method, on which the present invention builds, an electric high-frequency field is generated between the electrode faces and therewith in the process volume charged with a reactive gas, a high-frequency plasma discharge is generated. The one electrode face is herein comprised of a dielectric material and a high-frequency potential is applied to it with a specified distribution varying along the face. The distribution of the electric field in the plasma process volume is set through the potential distribution on the dielectric electrode face. In the method forming the basis, the substrate either forms the dielectric electrode face or the substrate is disposed at the second electrode face developed metallically. Furthermore, at the electrode face opposing the substrate the reactive gas is introduced into the process volume through an aperture pattern.
In recent years increased effort has been exerted to produce larger disk-form workpieces incorporating reactive high-frequency plasma-enhanced methods. One of the reasons was the wish to reduce the production costs. High-frequency plasma enhanced methods (PHfECVD) are employed for substrate coating or as reactive high-frequency plasma-enhanced etching methods. Said efforts can be seen in particular in the production of liquid crystal displays (LCD), of TFT or plasma displays, as well as in the field of photovoltaics, and therein especially in the field of solar cell production.
When carrying out such production methods by means of said high-frequency plasmas-enhanced reactive methods with the known use of areal metal electrodes opposing one another in parallel, each with a planar electrode face facing the process volume in a vacuum receptacle and applying the electric high-frequency field for the plasma excitation, it was observed that with substrates increasing in size and/or increasingly higher excitations frequency fHf the dimension of the vacuum receptacle, in top view onto the substrate, is no longer of secondary importance. This is especially true in view of the wavelength of the applied high-frequency electromagnetic field in a vacuum. The distribution of the electric high-frequency field in the vacuum chamber, viewed parallel to the electrode faces, becomes inhomogeneous and to some extent differs decisively from a mean value, which leads to the inhomogeneous treatment of the workpiece positioned on one of the electrode faces: during etching an inhomogeneous distribution of the etching action results, with coating, for example of the layer thickness, the layer material stoichiometry, etc. Such significant inhomogeneities in the treatment are not acceptable for some applications, such as in particular in the production of said liquid crystals, TFT or plasma displays, as well as in photovoltaics, and here especially in the production of solar cells. Said inhomogeneities are more pronounced the more said dimension or extent of the receptacle approaches the wavelength of the electric field in the receptacle.
To solve this problem, in principle different approaches are known:
U.S. Pat. No. 6,631,692 as well as US A 2003/0089314 discloses forming the plasma process volume between two metallic electrode faces, which are opposite one another, and to shape one or both of the opposing metallic electrode faces.
The metallic electrode face, which is opposite the substrate disposed on the other electrode face or the metallic electrode face on which the substrate is supported, or both opposing metallic electrode faces are developed such that they are concave. This known approach is shown schematically in FIG. 1, in which denote:    1a and 2b: the metallic electrode faces opposing one another above the process volume, between which faces the high-frequency field E is generated,    Er, Ec: the electric field, respectively generated peripherally and centrally.
A physically fundamentally different approach, on which also the present invention builds in order to solve the above problem, is known from U.S. Pat. No. 6,228,438 by the applicant of the present application. The principle of this approach according to U.S. Pat. No. 6,228,438 will be explained in conjunction with FIG. 2, which, however, represents a realization not disclosed in said document. But this realization is intended to serve as the foundation for an understanding. One of the opposing electrode faces 2a, for example, as depicted is metallic. The second electrode face 2b, in contrast, is comprised of the dielectric material, for example a dielectric areal thin plate 4. Along the dielectric electrode face 2b a potential distribution φ2b is generated, which, in spite of a constant distance between the two electrode faces 2a and 2b, in the process volume PR yields a desired local field distribution, as shown for example in the margin region a stronger field Er than in the center region Ec. This can be realized, for example as shown in FIG. 2, thereby that a high-frequency generator 6 is coupled to the dielectric plate 4 across capacitive elements CR, Cc differently, according to the desired distribution. In the implementation depicted in
FIG. 2, however not disclosed in said U.S. Pat. No. 6,228,438, of the principle realized in said patent, the coupling capacitors CR must be selected to have higher capacitance values than the center capacitors Cc. The development of the capacitors CR or Cc is solved according to U.S. Pat. No. 6,228,438 in the manner depicted in FIG. 3. A dielectric 8 is provided which, on the one hand, forms the electrode face 2b according to FIG. 2, which simultaneously, due to its locally varying thickness d, with respect to a metallic coupling face 10 forms the locally varying capacitances CR,C provided according to FIG. 2. The dielectric 8 can therein, as shown in FIG. 4, be formed by a solid dielectric or by an evacuated or gas-filled hollow volume 8a between metallic coupling face 10 and a dielectric plate 4 forming the electrode face 2b. It is essential that in this hollow volume 8a no plasma discharge is developed.
The present invention builds on the known method according to U.S. Pat. No. 6,228,438, which was explained in principle in conjunction with FIGS. 2 to 4. In this approach the question arises of where to place a substrate to be treated in the process volume PR, wether at the dielectric electrode face 2b or at the metallic electrode face 2a. Said U.S. Pat. No. 6,228,438 teaches placing dielectric substrates on the electrode face 2b or electrode face 2a, but (column 5, line 35 ff) substrates with electrically conducting surface on the metallic electrode face 2a. 
It is furthermore known from said document to introduce reactive gas into the process volume and specifically distributed from an aperture pattern at the electrode face opposite the substrate to be treated. Therefore, if a dielectric substrate according to FIG. 3 or 4 is disposed on the electrode face 2b, the aperture pattern with the gas supply is to be provided on the side of the metallic electrode face 2a. If the substrate is disposed on the metallic electrode faces 2a, the aperture pattern for the reactive gas is to be provided on the side of the dielectric electrode face 2b. In this case, as is clearly evident in FIG. 4, the hollow volume 8a can be employed as equalization chamber and the reactive gas is only introduced through the metallic coupling configuration with coupling face 10 into the equalization chamber 8a and through the aperture pattern provided in dielectric plate 4 into the process volume Pr. However, it is entirely possible to fill the hollow volume 8a with a dielectric solid, be that with the material forming the dielectric electrode surface 2b or one or more to some extent different therefrom and to supply the aperture pattern through this solid via distributed lines with the reactive gas.
It can fundamentally be assumed that the combination of the aperture pattern for the inflow of the reactive gas into the process volume and the dielectric 8 or 8a according to FIG. 3 or 4 on a single electrode configuration requires significantly more effort than providing the aperture pattern on the electrode face 2a according to FIG. 3 and placing the substrate to be treated on the dielectric electrode face 2b or even developing the dielectric electrode face 2b by a dielectric substrate itself.
For it appears advantageous to separate functionally the gas inlet measures with the aperture pattern and the measures for affecting the electric field, i.e. if possible to deposit the substrate to be treated on the dielectric electrode face 2b or to structure the dielectric electrode face 2b at least partially by the substrate and to shape the gas inlet conditions through the aperture pattern on the metallic electrode face 2a. 